1. Field of the Invention
This invention relates generally to foot powered vehicles such as bicycles and stationary exercise bicycles and similar devices, and in particular, to crank adjusting mechanisms for such devices.
2. Background Description
Devices for the adjustment of the stroke length for a bicycle crank have been necessary for some time and many and various devices have been designed to accomplish such a result. One such arrangement is disclosed in U.S. Pat. No. 363,522, granted May 24, 1887 for "A Crank for a Velocipede", inventor Jay. Knous. A crank arm with a series of continuous apertures for accepting the pedal pin are positioned near the distal end of the crank arm. The threaded end of the pedal pin extends through the apertures and is secured to the crank by a threaded nut.
An adjustable crank is also shown in U.S. Pat. No. 421,969, granted Feb. 25, 1890, to inventor S. N. Pond. In this case, the end of the pedal pin is shaped to slide up and down in a guide and has a threaded aperture centered therein for accepting a threaded rod that is used to move the pedal up and down. A pair of beveled pinion gears are attached to the threaded rod, one being positioned within the guide area and the other being positioned at the top of the crank adjacent the bearing housing. Also a pair of racks are mounted on a plate or collar that is designed to slide vertically on a fork to which the crank end is attached. The top rack can be positioned so as to engage with the inboard pinion and the lower rack may be positioned to engage with the outboard pinion. The top rack, when engaged with its associated pinion, tends to raise the pedal, that is shorten the stroke, and the other tends to lengthen the stroke. In this way, the pedal stroke can be adjusted to suit the rider and once this is accomplished, the racks are positioned so as to not engage the pinions when the operator pedals the bike. A problem with this device is that in order to make the installation on a bicycle, it is necessary to form a hole in the shaft to permit passage of the rod or bar on which the pinions are attached. Further, it would appear that the device is connected directly to the drive wheel of the velocipede and not to the standard crank arm employed in present day bicycles.